The present invention pertains to bimorph benders and, in particular, to an improved means for mechanical coupling to such benders.
Piezoelectric bimorph benders are well known in the art, especially when used in transducer applications. Such benders are normally comprised of a pair of circular piezoelectric elements having diametrically opposed surface portions. Electrodes are formed contiguous with each element surface and extending over a substantial area thereof. The two discs are held in fixed space relationship by a center vane member sandwiched therebetween, and affixed thereto. Upon application of electrical signals to the electrodes, the bender dishes, with maximum displacement occurring at the bender's central location.
The bender's mechanical load has commonly been bonded to the central portion of one disc surface. This construction has proven fault prone since, especially at high power levels, the ceramic may be torn from the center vane. Further, since both ceramic discs contribute to the electromechanical energy conversion, coupling to one disc alone does not provide maximum energy transfer to the load.
Effective coupling to the bender would be accomplished if the driver had a hole in its center, such that the load could be attached thereto as with a nut and bolt. Prior art attempts to fabricate a hole in the center of a bender driver have proven unsuccessful, mainly because the hole equalizes some of the dynamic stresses in the bender thereby reducing the electromechanical coupling factor. The loss in coupling factor cannot be tolerated, since the design objective of piezoelectric motors is to make the driver as efficient as possible with a high power handling capability.